The influence of cyclometalated ligand motifs on the solid-state assemblies and luminescent properties of Pt(II)-Tl(I) complexes

Abstract

We have synthesized the HC^N ligand, 1-(naphthalen-2-yl)-1H-pyrazole (1A), and carried out its cyclometalation reaction with [{Pt(ν-CH)(μ-Cl)}] to give [{Pt(Naph^N)(μ-Cl)}]. This process takes place via the intermediate [Pt(ν-CH)Cl(HNaph^N-κN)] (2A) which could be isolated and fully characterized. Compound [{Pt(Naph^N)(μ-Cl)}] and the analogous N-heterocyclic carbene complex [{Pt(Naph^C*)(μ-Cl)}] (HNaph^C*-κC∗ = 3-methyl-1-(naphthalen-2-yl)-1H-imidazol-2-ylidene) were used to prepare the bis-cyanide anionic derivatives NBu[Pt(Naph^E)(CN)] (E = N 4A, C* 4B) which subsequently react with TlPF to afford the corresponding complexes [PtTl(Naph^E)(CN)] (5A and 5B). The X-ray structures of 5A and 5B show the presence of 2D extended networks created by organometallic >PtTl(Naph^E)(CN)> entities, each one containing a Pt→Tl dative bond (d Pt-Tl = 3.0205(3) Å 5A, 2.9395(4) Å 5B). These units are linked together through additional Tl···NC and Tl···πcontacts, which, in the case of 5B, renders a stair-like arrangement. NBO charge distributions analysis on 4A and 4B shows a small negative charge on the Pt center for 4B, while positive for 4A, indicating the more electron donating character of the carbene with respect to the pyrazole group. Pt and C NMR spectra of NBu[Pt(Naph^E)(CN)] (E = N 4A′, C* 4B′) account for this difference. Photophysical analysis has been performed for 4A/B and 5A/B regarding the Naph^E fragment. The emissions of 4A and 4B in CHCl at 77 K present similar profiles and have been assigned to ILCT [π(Naph^E) → π*(Naph^E)] excited states. The green emission of 4A in poly(methyl methacrylate) (PMMA) film (5 wt %) affords a photoluminescence quantum yield (PLQY, φ) of 82%. In the solid state, the vibronic emissions of 5A (λ = 528 nm) and 5B (λ = 561 nm) are red-shifted in relation to their precursors (λ = 488 nm 4A, 530 nm 4B) and are mainly attributed to MM′LCT [d/s σ*(Pt,Tl) → π*(Naph^E)] excited states.